1 Field of the Invention Resistance to infectous disease is the result of both innate and acquired immunity. Innate immunity is nonspecific and involves the body's defense mechanisms such as a the skin barrier, secretions, and the cough reflex, whereas acquired immunity is very specific and often involves the production of a specific response (antibody) to a specific stimulus (antigen) which may be a foreign substance or a natural substance which has gone awry.
The complement system serves as one part of the immune system and is also activated both by specific substances (antibody) and by the nonspecific substances (e.g. yeast wall and pneumococcal cell wall). The complement response involves a series of biochemical reactions in which one protein acts on another, which in turn acts on another and so on. These proteins are designated by a alphabetical abbreviations and numbers commonly accepted in the field of immunology (e.g. Cl, B, P). Ultimately, this cascade may lead to the entrapment and/or cytolosis (destruction) of the offending substance. There are a number of other mechanisms by which the body defends itself, but for the purposes of brevity and simplicity, these have been omitted here.
As with any body function, the immune response does not always work perfectly or in the best interests of the individual. Allergies, for example, are the result of an overzealous immune response and are often quite harmful to the individual. Organ transplant rejection, on the other hand, is an example of an appropriate immune response which is detrimental to the individual. Similarly, there are a whole variety of autoimmune diseases which result from the immune response attacking the individual's own cells.
These immune and autoimmune disease represent a class of disease which are often difficult to treat effectively. lthough there are a number of drugs which exist to treat them, none are adequate to control or inhibit complement activation. The inhibition of complement may be very important in a variety of these diseases because as the complement system becomes active, there may be destruction and removal of cells and substances, which is detrimental to the individual. It is useful, therefore, to have substances which can be administered to patients to prevent active complement activation.
Diseases in which such a substance may be therapeutically useful include paroxysmal nocturnal hemoglobulinurea, rheumatoid arthritis, (in which the substance might be administered directly to a joint capsule to prevent complement activation), and hereditary angioedema, (in which deficiency of a complement control protein leads to very active complement consumption).
Heparin, a polydisperse sulfated polysaccharide, is used primarily as a blood anticoagulant during many medical and surgical procedures. Although this is heparin's primary activity, it also displays other secondary activities such as its ability to inhibit complement activity. However, heparin's potency as an anticoagulant has made its use as a complement activation inhibitor problematic. The use of anticoagulant active heparin for the treatment of immune related disorders can result in hemorrhagic complications.
Heparin's anticoagulant activity has been demonstrated to be associated with the presence in its structure of a specific sequence for the binding of antithrombin III. Once bound to heparin, antithrombin III can then inhibit a number of blood coagulation factors, and thus prevent coagulation of blood. Several approaches have been used to separate heparin's anticoagulant (primary) activity from its complement cascade inhibition (secondary) activity. The removal of this antithrombin III binding sequence from heparin permits the exploitation of this drug for the treatment of immune related disorders Such disease states for which this drug would be useful include septic shock, rheumatoid arthritis, lupus and systemic lupus erythematous.
Heparin's anticomplement activity is mediated by binding to a variety of complement proteins and thereby regulates both the classical and alternate amplification pathways. Heparin inhibits a portion of the complement cascade by inhibiting generation of the cell bound amplification pathway C3 convertases, C3b,Bb, C3b,Bb,P and C3b,Bb,Nef. It also acts as a complement inhibitor by interfering with the binding site on C3b for B. Furthermore, it prevents the consumption of B by D in the presence of C3b again indicating a direct action on C3b.
2. Prior Art
Heparin has been used for the last half century as an anticoagulant. Commercial heparin, with an average molecular weight of 10,000-14,000, also possesses a multiplicity of other biological activities including an ability to regulate complement activation. The structure-activity relationship for heparin is well understood for anticoagulant activity, but is poorly understood with effect on the complement system. Moreover, heparin's anticomplement activity is heretofore been coupled with its anticoagulant activity which often is an undesirable side effect.
Therefore, it is desirable to provide isolated components of heparin which have high anticomplement activity with low anticoagulant activity.